622 Trow. — The Karyology of Saprolegnia. 
years, I should have at once concluded that both species are 
simply forms of one produced by somewhat different external 
conditions of life. Under the circumstances, however, I con- 
cluded, at least provisionally, that the cultures were impure, 
and that the oogonia with antheridia might reasonably be 
referred to S. mixta , and the oogonia without antheridia to 
either mixta or S. Thureti. These are, of course, respectively 
androgynous and completely apogamous forms. 
It would have been obviously entirely outside the province of 
this research to attempt the decision of the specific identity 
of S. Thureti and 5. mixta ; the work would probably have 
required many years to carry out, and the results would not 
have had, so far as I can see, the slightest effect in the solution 
of the problems investigated in this paper. As a matter of 
fact, it may be regarded, apart from the difficulties of descrip- 
tion, as a fortunate circumstance that the material contained 
the antheridium-bearing form. 
In the following descriptions I shall refer to the antheridium- 
bearing oogonia as those of S. mixta , and to the others as 
those of apogamous oogonia of 5. Thureti and S. mixta. 
The most beautiful results were obtained during the investi- 
gation of 5. mixta , but simply because by this time the 
method of staining adopted had reached its highest degree of 
efficiency. So far as I am able to judge at present, the 
karyology in the three forms, with one important exception, is 
identical. Most of my figures, however, refer to 5. mixta , for 
the reason already stated. 
The zoospore. Structure of the nucleus. Zoospores which 
have come to rest and clothed themselves with a cell-wall are 
generally abundant in the preparations. They fix well and 
stain easily, and I have consequently come to regard them as 
a kind of index to the value of the preparations. Each 
zoospore contains a quantity of granular protoplasm which is 
of a more or less spongy texture. The granules or micro- 
somata are frequently of considerable size, and stain readily, 
although not with so deep a colouration as the nucleus. The 
nucleus is spherical and is bounded by a distinct nuclear wall. 
